Synthesis of carbazole from 0-aminobiphenyl with alumina as tar inhibitor



' phase with a mmimem tommtion ofizt Patented Aug. 16, 1949 ounce simmers; F osnmzom r 1mm 7;

oimmomeimm ALUMINA? ASTARJNHIBIIOR v fiuetiiew cdhwerysta LouiwMoe assign: to

'Mbnsmtwchmieai Company, St. Louis, Mm awemrztion ofi flehware e nutmeg;mi imummwmbeemm;

6 Claims (01. 560415) usemeannesin-conjimction-iwltli hlghi ieim i perature-"vapor phasemperatibhs, thehazard from r fires and explosions in vapopphase operations-,8 and othen problems-make new methods qtmanu-c facturer of carbazole'drom o-samiriobiplienyi: ilesirablefi I Efforts have-been made'toa'obta'i n carbaz ole by fusing o-aminobiphnyh'witlfa nitio com pound of the benzene eeries et temperatures in the -range 'et r3e9a359 l --Thi's:pr0c6Ss results-in thglfgpmabjm rsm'gemoetiions nt esompleietaew residue and-m mmde eazbezolepremise mess-i??- centaminateirand xiimeult' -to purifyu Moreweissince the nitre eer.nnomucl;exmi ltem'd exide ticn agenfiln'hifi apparently eonvertecv to fa eompl'eie-tezny miatureimmlmrhich no' uzeihle reductacambeweeowered,ehc co tni this matew 0weemememmemwmm mammals: a

tumm -ide an 'impem ed {)fflGCSS totimaklne b31618 hi sthkeiraoxidetiom'ofih aminobipiienyly immelliquimphama Y 1 if Anothezsobjeet isitmpmvxde au'imprmed metha 0d; m wadizlngn ro-aminobiphenylrnin "itlieidiquidr Other:

2 range of 300-400 C. As'aTu-rther embodiment ch -am z-in ventlong the apmcess isdesirablyicondmted iin 'rthenpresence 'ofran inhibitor of tar formations I :have found ztliat either-crystalline alamina hydrate for graphite r aref excellent in a hibitnrs of ::tar1'ormatiominflahe process of I the" pnesent iriventien and anemia-l mme effective than 1 any other substances: tested-Tier this purpose.

'In -"the :process 101 :the': I present rin venticn; 1

may-beIsuppIied-tothe reaction zcne underPressure, iforl "example; ati'a, pressure in the 1 range of 16. 35 ebsi pemsqzai ,:am-=ldesirabiy fin the 'range' from tli reactiom zone'il 'I 'he-alr- =streami'may'be passed thfmugm the re'actien *mixtuse although 2 ms is not essentlai when th'e 'reaction- 'mmture isi-yigerously agitated; On' the othlar name: it*

may be desirable toemp1oy the 'a-i-rstream" as a means for eiieetink atiieast part bf tlie agitatiom *for examples by passingilthelstream" through the:

reaction mixture. The volume of air brought into contact with the reaction mixture by any desired-means durlng the course of' the reaction should-be in excess of 'tliecry 'for -the oxidatiom -01" wamixiebiphenyr to ca'rbazole and- "desirably appmximately e to *6 *times 'the theoretical *re-' quiremexiti- A suitable 'rate of flo'w bran-for this purpose may be in the range of 2 to 22511. ft. per 100 lbs. of o aminobiphenyl per minute. This rate of flow may be varied according to tliwartieiuarconditions employedin"eachfinstence'i? Th tar' inhibitor, 'fo'i exampleitli'e' crystelll'nealumina= hydi'eite' and "graphite; are desirably em payed inf ameunts of 0.8 parts' by'weight or more per -10Wpart's by weight of '-'o-am'in'ebiplienyl' "although smaller or larger amounts may be"employed, for exampleywitlbvalriations in the temperature, pressure, and agitation. I have found 40* that increasing" ithereaction temperature above objects will become:apparenturomitltezsoltewinm description and examples,

According to the present invention, generally stated; o-amieebipherm ismxidlzed iojicenbazole in goou yieids' -hy intimately contacting maminow biphenyl -lrr tlie iiquid -fipliaswwm' ais, i101 exam: me; my agitating'mmmebipnenmimthe meme: state-in themreseme use streamer-Mr orsetheif oxygen#contaimwfsds atiirtempsmiire anirtne 280* G. "resiflts iii theiformation of less tar; al thougli'thisis"accomplishedat the expense of lower conversionsof"- o-ami'nobiphenyr' to carba'-- zoleL" I -havealso" founwthat" the presence 'of 5 crystalline alumina hydrate orgraphite inamoimts 'iereinbefore set" forth'resu1ts in' very mummies-mitten of th ta r formation; and partieuleeiy in th temperature range of 330 3-75 :C.-

Otlier sub'starice" -whichvmz'az flne" employed as tareinmbiters insthe pmeess m the present" in vention are metal salts such as the nitrates, chromates, benzoates, succinates, and monobutyl-butyloxy-succinates. of metals such as manganese, cobalt, aluminum, copper, iron, lead, and sodium, and oxides such as titanium oxides. However, none of these substances are in the same category as crystalline alumina, hydrate and graphite with regard to effectiveness in inhibiting tar formation in the process.

The carbazole formed by the process-of the present invention may be recovered by any-desired procedure, for example, the reaction mixture may be dissolved in hot o-xylene and the solution may be filtered while hot.v .The ,carba It will be observed from Table I that the minimum zole crystallizes from the filtrate and jisith'en filtered off, washed with o-xylene and dried. Other suitable solvents such as hot o-dichlorobenzene may be employed in place of o-xylene for the crystallization operation. v

The following examples will serve to illustrate the novel process of the presentinvention.v Thesev examples are merely illustrative and are not'to be construed as limiting the invention as defined in the appended claims.

EXAMPLE I. A mixture of 250 grams of o-aminobiphenyl and 4 grams of finely divided crystalline alumina hy-' drate is heated to a temperature of 375 C. in a jacketed, heated autoclave. The liquid'reaction mixture is strongly agitated, for example, by means of a rotary agitator at 960 R. P. M. A stream of air at a pressure of 50 lbs. per sq. in. is admitted to the autoclave at the rate of 2 cu. ft. per. minute. 'The pressure in the autoclave is maintained at approximately 50 'lbs. per sq. in. and the reaction mixture is maintained at 375 C. for 6 hours. Thereafter, the pressure is released and the reaction mixture is dissolved in hot o-xylene, filtered-while hot and allowed to cool. 'I'hecrystalline carbazole which separates is filtered-off, washed with cold o-xylene and dried.-

A 26.5% conversion of o-aminobiphenyl tocarbazole is thus obtained representing a yield based on o-aminobiphenyl consumed of 97.5%.

' EXAMPLE II The process of Example I was repeated using 4 grams of fine flake graphite in place of the .crystalline alumina hydrate. A 28.2% conversion of o-aminobiphenyl was obtained representing a yield based on o-aminobiphenyl consumed of 93.4%.

EXAMPLE III 7' The process of Example I was repeated omitting the crystalline alumina hydrate tar inhibitor andoperating the process at 360 C. and 52 lbs. per sq. in. for 8 hours. A 34.5% conversion of oaminobiphenyl to carbazole was obtained representing a yield of carbazole on o-aminobiphenyl consumed of 87.2%.

EXAMPLE IV A series of runs were made according to the process described in Example I in which 4 grams of crystalline alumina hydrate per 250 grams of o-aminobiphenyl were employed as tar inhibitors and the time of reaction was 8 hours. The rate of agitation was 960 R. P. M., the pressure in the autoclave was maintained at 45-50 lbs. per sq. in. by controlling the pressure of the air flow into the; autoclave and the temperature of the reaction mixture in respective runs was varied from 280 C. to 375C. "The results are tabulated in Table I.

Table I Percent Conver- Temp. of sum 9 Yield on o-amlno- Reaction blphenyl biphenyl Con- Migzture, sumed (Percent of To To Carba- Theory) Tar zole tar formation was obtained under the conditions of the reaction when the temperature of the reaction mixture was 375 C. The residual o-aminobiphenyl may be recovered in plant practice from the reaction mixture by distillation after removal EXAMPLE V A seriesof runs were made according to the procedure of ExampleI in which'the amount of crystalline alumina hydrate tar inhibitor was varied from2-8 parts by weight per' 250 parts by weight of o-aminobiphenyl. The time of reaction was 6 hours, the average pressure was55 lbs. per sqin., the rate of agitation was 960 R. P. M., and the temperature of the reaction'mixture was maintained in each instance in the range 'of 370-2" C. The results are tabulated in Table II.

" Table II Percent Conversion Temp. of of o-aminobiphcnyl Yield on o-amino- Amount of Reaction biphenyl 0onl'nhibitor Mixture, snmed. Percent of i C. To To Oarba- Theory Tar zole None at f gslo 22.9 85. 2 2. 0 V 37].- 1.7 23. 9 93. 5 4. 0 370 1. 3 23. 8 94. 8 8. D 372 1. 4 22. 8 94. 4

. I ExAMPLE VI A series of runs were made according to the procedure of Example I'in which the rate of agitation was 480 R; P. M., the time of reaction was 24 hours, the temperature of the reaction mixture was maintained at 305-310 C., and the pressure in the autoclave was maintained at 49-52 lbs.

per sq. in. In successive runs; respective tar in-' nitrate,- copper nitrate, cobalt nitrate and ferric. Ammonium chromate' nitrate, titanium oxide. was also employed; In each instance'large portions of tar were formed and the yields of carbazole' based on o-aminobiphenyl consumed ranged from 29% to less than 60%.

EXAMPLE A series of runs were made according to the method of Example'I in which the pressure in the autoclave was varied. The temperature of the reaction mixturewas maintained. at 375 C. and the rate of agitation was maintained at 960 R. P. M. The tar inhibitor employed was 4 grams of crystalline alumina hydrate, per 250 grams of o-aminobiphenyl. The pressure in the autoclave was varied in successive runs from lbs. per sq. in. to 75 lbs. per sq. in. In each run carbazole was found to have been produced in substantial yields. The range of 30-60 lbs. per sq. in. was found to give very satisfactory results in terms of yield and quality of product.

The process of the present invention as illustrated in the aforescribed examples is desirably operated at a reaction temperature in the range of 330-375 C. with strong agitation and with an excess of air over the theoretical requirement in order to obtain a maximum conversion of o-ami=- nobiphenyl to carbazole with a minimum of tar formation and a maximum yield of carbazole based on o-aminobiphenyl consumed. Moreover, for maximum inhibition of tar formation, the process is desirably operated in the presence of finely divided crystalline alumina hydrate or of graphite to the extent of approximately 4 parts by weight of inhibitor to 250 parts by weight of liquid phase with an excess of air under pressure in the presence of at least 0.8 part by weight of crystalline alumina hydrate per 100 part by weight of o-aminobiphenyl at a temperature in the range of 330-375 C. for a period of time in the range of 6-24 hours, passing said air into the reaction mixture at a rate in the range of 2-22 cu. ft. per 100 lbs. of o-aminobiphenyl per minute, and subsequently recovering carbazole from the reaction mixture.

4. A process of making carbazole comprising intimately contacting o-aminobiphenyl in the liquid phase with an excess of air under pressure a in the presence of crystalline alumina hydrate at o-aminobiphenyl, or at least 1.6 parts by weight per 100 parts of o-aminobiphenyl. Variations in the conditions under which the process is operated, depending upon the nature and size of the equipment and the other factors involved, are contemplated as being within the scope of the present invention and the invention is not to be construed as being limited to the specific conditions, agents, or apparatus described in the examples except as defined in the appended claims.

I claim:

1. A process of making carbazole comprising intimately contacting o-aminobiphenyl in the liquid phase with an excess of an oxygen-containing gas under pressure in the presence of crystalline alumina hydrate at a temperature in the range of 300-400 C., for a period of time in the range of 6-24 hours and subsequently recovering carbazole from the reaction mixture.

2. A process of making carbazole comprising intimately contacting o-aminobiphenyl in the liquid phase with an excess of air under pressure in the presence of 2-8 parts by weight of crystalline alumina hydrate per 250 parts by weight of o-aminobiphenyl at a temperature in the range of 300-375 C. for a period of time in the range of 6-24 hours, and subsequently recovering carbazole from the reaction mixture.

3. A process of making carbazole comprising intimately contacting o-aminobiphenyl in the a temperature in the range of 330-375 C. for a period of time in the range of 6-24 hours, passing said air through said reaction mixture at a rate in the range of 2-22 cu. ft. per lbs. of o-aminobiphenyl per minute, and subsequently recovering carbazole from the reaction mixture.

5. In the manufacture of carbazole by the airoxidation of o-aminobiphenyl in the liquid phase, the step comprising intimately contacting o-aminobiphenyl in the presence of crystalline alumina hydrate and in the presence of air at a pressure in the range of 10-75 lbs. per sq. in. and a reaction temperature in the range of 300-3'75 C. for a period of time in the range of 6-24 hours.

6. In the manufacture of carbazole by the airoxidat-ion of o-aminobiphenyl in the liquid phase, the step comprising intimately contacting o-aminobiphenyl in the presence of at least 0.8 part by weight of crystalline alumina hydrate per 100 parts by weight of o-aminobiphenyl and in the presence of air at a pressure in the range of 30-60 lbs. per sq. in. and a reaction temperature in the range of 300-375 C. for a period of time in the range of 6-24 hours.

COURTNEY CONOVER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS pages 358 to 360 (1938). (Copy in 260-315.) 

